Myth: Exercising at a low intensity burns more fat

TRUTH: Anyone who has ever been on a treadmill has probably noticed that there is a “fat burning workout” option that keeps your heart rate at a lower level than the cardio workout. Given that it’s called a “fat burning workout”, it’s logical to assume that means that you’ll burn more fat by keeping your heart rate in that recommended range. However, the most fat-burning workout is actually just the opposite.

The “fat burning workout” will burn more fat while you’re exercising, because at lower heart rates, your body uses fat as fuel. It’s an aerobic workout, which means that your body is using oxygen to break down stored fat for energy. When you workout more intensely, you’re working anaerobically (literally meaning without oxygen), which means that your body is using stored carbohydrate (aka glycogen) for fuel.

Ok, you’re done with the physiology instruction, what’s the point, right?! The point is this: exercising at a low intensity burns more fat right now. But overall, you’ll burn more fat if you work out more intensely. Why? Simple math.

Weight is a result of calories in vs. calories out. If you burn more calories than you consume, you’ll lose weight. So, the more calories you burn, the more fat you’ll lose overall. So, if I run for 30 minutes at a low intensity, maybe I’ll run 3 miles and burn about 200 calories. But, if I run for 30 minutes at a high intensity, maybe I’ll run 4 miles and burn about 275 calories. Clearly, burning more calories promotes more weight loss.

BOTTOM LINE: You should not take workout advice from a treadmilll. It’s all marketing – who wouldn’t want to read “If you get on this machine, you can burn all the excess fat you want. Just don’t work too hard.” Weight loss or weight maintenance is about the calories out, not about the fuel source used during exercise. Ultimately, the harder you work, the more fat you’ll burn.